Chocolate that has ingredients like animal fats or alcohol is haram. If alcohol is used to clean the machinery that makes the chocolate bars, then that chocolate is also considered unfit for consumption for Muslims. If the glue used in the packaging is derived from animal fats, that also makes the chocolate haram. For chocolate to be classified as halal chocolate, not only must it not contain unlawful ingredients, but it cannot be processed or stored or transported in ways or facilities that are haram.
Basically, the only way it wouldn't be halal is if they used alcohol to clean the machines, used an alcohol derivative to flavor the chocolate (and Hershey doesn't for their dark chocolate), used an animal fat derivative to bind the rice coating to the chocolate, or they somehow violated it in shipping or packaging.
A lot of halal stuff is halal on basis of it not including gelatin, pork, or alcohol. There is also an interesting debate on halal and kosher meats, in that an animal has to be slaughtered in such a way that it would be considered inhumane... which is why it's illegal in parks of Europe.